This application relates to automatic test systems for digital electronic converters and statistical methods for testing analog-to-digital converter and digital-to-analog converters. More particularly, this invention relates to a method for calibrating an analog-to-digital converter employing statistical amplitude density functions. In addition, the techniques described herein may be used in analysis of analog-to-digital and digital-to-analog converters.
Converters between the digital and analog signal domains are employed to interface digital electronic circuitry and analog devices. Accuracy of conversion, gain and repeatability in the process of conversion are matters of concern. One method of testing a digital-to-analog converter is to apply a digital signal to its input and obtain an analog output signal, then to apply the analog signal to the input of an analog-to-digital converter to recover a digital signal and then to process the output signal to determine its statistical characteristics. The characteristics of the output signal in terms of a statistical description provide an indication of the accuracy of the digital-to-analog converter.
Such an analysis presupposes the use of a calibrated or "characterized" analog-to-digtal converter. By "characterized" it is meant that the transfer characteristic either from the input to the output or from the output to the input is known to an accuracy commensurate with the accuracy of the device to be analyzed. The transfer characteristic may be described in terms of premeasured weighting coefficients of a polynomial of the powers of two or in any other form which accurately reflects the process of converting a signal x into a signal y, or alternatively, a signal y into a signal x. For example, such a characterization may be formulated in terms of two-state orthogonal functions such as the Walsh functions.